Multilayered printed circuit board and method for manufacturing the same

ABSTRACT

A multilayered printed circuit board or a substrate for mounting a semiconductor device includes a semiconductor device, a first resin insulating layer accommodating the semiconductor device, a second resin insulating layer provided on the first resin insulating layer, a conductor circuit provided on the second resin insulating layer, and via holes for electrically connecting the semiconductor device to the conductor circuit, wherein the semiconductor device is accommodated in a recess provided in the first resin insulating layer, and a metal layer for placing the semiconductor device is provided on the bottom face of the recess. A multilayered printed circuit board in which the installed semiconductor device establishes electrical connection through the via holes is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims the benefit ofpriority to U.S. application Ser. No. 11/580,165, filed Oct. 13, 2006,the entire contents of which are incorporated herein by reference. U.S.application Ser. No. 11/580,165 is based on and claims the benefit ofpriority to Japanese Application No. 2005-300349, filed Oct. 14, 2005.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a multilayered printed circuit board inwhich an electronic component (semiconductor device) such as an IC isinstalled and to a method for manufacturing the same.

2. Background Art

Examples of a multilayered printed circuit board in which asemiconductor device is installed include multilayered printed circuitboards disclosed in Japanese Unexamined Patent Application PublicationNos. 2001-339165 and 2002-050874. The multilayered printed circuitboards disclosed in these patent documents include a substrate having arecess for embedding a semiconductor device, a semiconductor deviceembedded in the recess of the substrate, an insulating layer provided onthe substrate so as to cover the semiconductor device, a conductorcircuit provided on the surface of the insulating layer, and via holesprovided in the insulating layer so as to electrically connect theconductor circuit to pads of the semiconductor device.

In such a known multilayered printed circuit board, external connectionterminals (such as PGA or BGA) are provided on the surface of theoutermost layer. The semiconductor device installed in the substrate iselectrically connected to the outside via the external connectionterminals.

SUMMARY OF THE INVENTION

In a multilayered printed circuit board according to an embodiment ofthe present invention, even when a substrate for accommodating asemiconductor device is composed of a resin, electrical connectivity andconnection reliability can be ensured. In addition, in a reliabilitytest, connection reliability between pads of the semiconductor deviceand a conductor circuit including via holes that are connected to thepads can be ensured in the multilayered printed circuit board.

An embodiment of the present invention provides a multilayered printedcircuit board including a semiconductor device, a first resin insulatinglayer accommodating the semiconductor device, a second resin insulatinglayer provided on the first resin insulating layer, a conductor circuitprovided on the second resin insulating layer, and via holes forelectrically connecting the semiconductor device to the conductorcircuit, wherein the semiconductor device is accommodated in a recessprovided in the first resin insulating layer, and a metal layer forplacing the semiconductor device is provided on the bottom face of therecess.

An embodiment of the present invention provides a multilayered printedcircuit board including a semiconductor device, a first resin insulatinglayer accommodating the semiconductor device, a second resin insulatinglayer provided on the first resin insulating layer, a conductor circuitprovided on the second resin insulating layer, and via holes forelectrically connecting the semiconductor device to the conductorcircuit, wherein the semiconductor device is accommodated in a recessprovided in the first resin insulating layer, a metal layer for placingthe semiconductor device is provided on the bottom face of the recess,and the second resin insulating layer includes a fiber substrate.

An embodiment of the present invention provides a multilayered printedcircuit board including a semiconductor device, a first resin insulatinglayer accommodating the semiconductor device, a second resin insulatinglayer provided on the first resin insulating layer, a conductor circuitprovided on the second resin insulating layer, and via holes forelectrically connecting the semiconductor device to the conductorcircuit, wherein the semiconductor device is accommodated in a recessprovided in the first resin insulating layer, a metal layer for placingthe semiconductor device is provided on the bottom face of the recess,and the area of the metal layer is larger than the area of the bottomface of the recess.

An embodiment of the present invention provides a multilayered printedcircuit board including a semiconductor device, a first resin insulatinglayer accommodating the semiconductor device, a second resin insulatinglayer provided on the first resin insulating layer, a conductor circuitprovided on the second resin insulating layer, and via holes forelectrically connecting the semiconductor device to the conductorcircuit, wherein the semiconductor device is accommodated in a recessprovided in the first resin insulating layer, a metal layer for placingthe semiconductor device is provided on the bottom face of the recess,and the wall surfaces of the recess are exposed.

An embodiment of the present invention provides a multilayered printedcircuit board including a semiconductor device, a first resin insulatinglayer accommodating the semiconductor device, a second resin insulatinglayer provided on the first resin insulating layer, a conductor circuitprovided on the second resin insulating layer, and via holes forelectrically connecting the semiconductor device to the conductorcircuit, wherein the semiconductor device is accommodated in a recessprovided in the first resin insulating layer, a metal layer for placingthe semiconductor device is provided on the bottom face of the recess,and openings constituting the via holes are filled with a conductivesubstance.

An embodiment of the present invention provides a multilayered printedcircuit board including a semiconductor device, a first resin insulatinglayer accommodating the semiconductor device, a second resin insulatinglayer provided on the first resin insulating layer, a conductor circuitprovided on the second resin insulating layer, and via holes forelectrically connecting the semiconductor device to the conductorcircuit, wherein the side faces of the recess form a tapered shapediverging from the bottom face upwards.

Furthermore, according to a method for manufacturing a multilayeredprinted circuit board according to an embodiment of the presentinvention, in a method for manufacturing a multilayered printed circuitboard wherein a semiconductor device is accommodated and fixed in afirst resin insulating layer, a second resin insulating layer and aconductor circuit are provided on the first resin insulating layer, andthe semiconductor device is electrically connected to the conductorcircuit through via holes, the method includes the steps of:

forming a first insulating resin substrate by forming on a first surfaceof the first resin insulating layer at least a conductor circuit and ametal layer having a predetermined area corresponding to the dimensionsof the semiconductor device to be accommodated, forming on a secondsurface of the first resin insulating layer at least a conductor circuitand an area that does not have the conductor circuit thereon, the areahaving a predetermined area corresponding the dimensions of thesemiconductor device at a position facing the metal layer, and formingvia holes for electrically connecting the conductor circuit on the firstsurface to the conductor circuit on the second surface;

bonding a second insulating resin substrate prepared by applying acopper foil on a first surface of a third resin insulating layer ontothe first surface of the first insulating resin substrate under pressureto integrate the substrates;

forming a conductor circuit on the first surface of the secondinsulating resin substrate and forming via holes for electricallyconnecting the conductor circuit formed on the first surface of thesecond insulating resin substrate to the conductor circuit formed on thefirst surface of the first insulating resin substrate;

forming, on the area of the first insulating resin substrate that doesnot have the conductor circuit thereon, a recess extending from thesurface of the first resin insulating layer to the surface of the metallayer so as to expose the surface of the metal layer;

accommodating a semiconductor device in the recess, and bonding andfixing the semiconductor device on the surface of the metal layerexposed in the recess, with an adhesive therebetween; and

covering the semiconductor device, forming the second resin insulatinglayer and a conductor circuit thereon, and then forming via holes forelectrically connecting the semiconductor device and the conductorcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a multilayeredprinted circuit board in which a semiconductor device is accommodatedand embedded according to the present invention.

FIG. 2 is a schematic cross-sectional view showing a multilayeredprinted circuit board having columnar electrodes provided on pads of asemiconductor device according to the present invention.

FIG. 3 is a schematic cross-sectional view showing a multilayeredprinted circuit board having an intermediate layer provided on pads of asemiconductor device according to the present invention.

FIGS. 4A to 4G are schematic cross-sectional views showing some steps ofmanufacturing a multilayered printed circuit board according to Example1 of the present invention.

FIGS. 5A to 5D are schematic cross-sectional views showing some steps ofmanufacturing the multilayered printed circuit board according toExample 1 of the present invention.

FIGS. 6A to 6D are schematic cross-sectional views showing some steps ofmanufacturing the multilayered printed circuit board according toExample 1 of the present invention.

FIG. 7 is a SEM image showing a cross section of the relevant part of amultilayered printed circuit board according to Example 3 of the presentinvention.

FIG. 8 is a schematic cross-sectional view showing a modification ofExample 1 of the present invention.

FIG. 9 is a schematic cross-sectional view showing another modificationof Example 1 of the present invention.

FIGS. 10A to 10D are schematic cross-sectional views showing some stepsof manufacturing a multilayered printed circuit board in which asemiconductor device is accommodated and embedded according to a relatedart.

FIG. 11 is a schematic cross-sectional view illustrating themultilayered printed circuit board according to the related art.

FIG. 12 is a schematic cross-sectional view illustrating the thicknessesof the exposed and non-exposed parts of metal layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A multilayered printed circuit board according to an embodiment of thepresent invention includes a semiconductor device, a first resininsulating layer accommodating the semiconductor device, a second resininsulating layer provided on the first resin insulating layer, aconductor circuit provided on the second resin insulating layer, and viaholes for electrically connecting the semiconductor device to theconductor circuit, wherein the semiconductor device is accommodated in arecess provided in the first resin insulating layer, and a metal layerfor placing the semiconductor device is provided on the bottom face ofthe recess.

Accordingly, by forming the metal layer on the bottom of the recess ofthe first resin insulating layer for accommodating the semiconductordevice, the depth of the recess can be made uniform. Therefore, thephenomenon in which the semiconductor device is accommodated andinstalled in the recess in a tilted manner can be prevented. Even whenthe substrate accommodating the semiconductor device is composed of aresin, electrical connectivity and connection reliability betweenconnection pads of the semiconductor device and the conductor circuitincluding via holes connected to the connection pads can be ensured.

In this embodiment, a conductor circuit may be provided on the firstresin insulating layer accommodating the semiconductor device, and theconductor circuit may be electrically connected to the conductor circuitprovided on the second resin insulating layer through via holes, andmore preferably via holes filled with a metal.

The thickness of the first resin insulating layer accommodating thesemiconductor device is preferably larger than the thickness of thesecond resin insulating layer. Accordingly, for example, warpage of thefirst resin insulating layer accommodating the semiconductor devicecaused by heat etc. does not easily occur. Therefore, connectivitybetween the semiconductor device and via holes connected thereto andreliability thereof can be easily ensured.

Furthermore, the conductor circuit on the second resin insulating layermay be provided so as to extend over an area that exceeds the boundarybetween the semiconductor device and the first resin insulating layeraccommodating the semiconductor device. Accordingly, the degree offreedom of wiring between the semiconductor device and the conductorcircuit connected thereto can be increased. Furthermore, since solderpads connected to the outside and via holes connected to thesemiconductor device are far from each other, the multilayered printedcircuit board is not easily affected by stress due to, for example, heatreceived on the solder pads functioning as an external connectionterminal. Therefore, it is believed that connectivity and reliabilitycan also be ensured.

Furthermore, the multilayered printed circuit board may further includevia holes connected to the metal layer, and heat generated on thesemiconductor device may be dissipated through these via holes connectedto the metal layer. That is, thermal vias connected to the metal layermay be formed, thereby dissipating heat from the semiconductor devicethat is received on the metal layer to the outside.

A multilayered printed circuit board according to an embodiment of thepresent invention includes a semiconductor device, a first resininsulating layer accommodating the semiconductor device, a second resininsulating layer provided on the first resin insulating layer, aconductor circuit provided on the second resin insulating layer, and viaholes for electrically connecting the semiconductor device to theconductor circuit, wherein the semiconductor device is accommodated in arecess provided in the first resin insulating layer, a metal layer forplacing the semiconductor device is provided on the bottom face of therecess, and the area of the metal layer is larger than the area of thebottom face of the recess.

According to this structure, the semiconductor device can be reliablyaccommodated. Furthermore, tolerance of misalignment during theformation of the recess of the substrate can be increased. Therefore,the depth of the recess provided in the first resin insulating layer canbe easily made uniform, and the multilayered printed circuit board isnot easily affected by other factors (for example, an effect ofirregularities during the formation of the recess and an effect duringthe formation of the metal layer).

In such an embodiment, at least a surface of the metal layer, thesurface being exposed on the bottom face of the recess, is preferablyplanarized. In this case, the thickness of an adhesive layer formedbetween the semiconductor device and the metal layer can be easily madeuniform. Consequently, the adhesiveness of the semiconductor device canbe made uniform, and the adhesiveness can be easily ensured even when areliability test is repeatedly performed under a heat-cycle condition.

The metal layer is preferably formed of a rolled copper foil. When themetal layer is formed using a rolled copper foil, the flatness of themetal layer can be easily ensured. In addition, the semiconductor devicecan be reliably accommodated, and the adhesiveness to the semiconductordevice can be easily ensured.

The wall surfaces of the recess of the first resin insulating layer arepreferably exposed. That is, when the semiconductor device isaccommodated, the wall surfaces of the recess are exposed. Accordingly,the semiconductor device can be reliably accommodated. Furthermore, theclearance between the wall surfaces of the recess and the side faces ofthe semiconductor device can be filled with an adhesive or another resininsulating layer, and bondability of the semiconductor device andelectrical connectivity of the semiconductor device can be easilyensured.

The metal layer is preferably exposed by laser processing. In this case,a recess having a uniform depth can be easily produced.

The thickness of the part of the metal layer exposed in the recess ispreferably smaller than the thickness of the non-exposed part of themetal layer. In this case, since a cavity is formed on the area wherethe semiconductor device is accommodated, it is believed that thesemiconductor device can be reliably accommodated.

The surface layer of the part of the metal layer exposed in the recesspreferably has a shiny surface. The adhesiveness between the metal layerand the semiconductor device can be easily ensured on the shiny surface.In addition, connectivity and reliability of the semiconductor devicecan be easily ensured on the shiny surface. Furthermore, the thicknessof an adhesive layer formed between the semiconductor device and themetal layer can be easily made uniform. Consequently, the adhesivenessof the semiconductor device can be made uniform, and the adhesivenesscan be easily ensured even when a reliability test is repeatedlyperformed under a heat-cycle condition.

Another surface of the metal layer, the surface being opposite to thesurface exposed in the recess, preferably has a matte surface. In thiscase, adhesiveness to another resin insulating layer can be easilyensured.

The semiconductor device is preferably bonded on the metal layer, withan adhesive layer therebetween. When the adhesive layer is provided onthe metal layer, a uniform adhesive layer can be easily formed, andbondability of the semiconductor device can be easily ensured.Furthermore, connectivity with via holes connected to the semiconductordevice and reliability can be easily ensured.

The adhesive layer is preferably in contact with the bottom face of thesemiconductor device and the bottom periphery of the side faces of thesemiconductor device. When the adhesive layer is in contact with thebottom face and the bottom periphery of the side faces of thesemiconductor device, the adhesiveness of the semiconductor device canbe easily ensured.

The metal layer is preferably installed in a substrate for accommodatinga semiconductor device in advance, or the surface of the metal layer ispreferably planarized. When the metal layer is installed in thesubstrate, the multilayered printed circuit board is not easily affectedby other factors (for example, an effect of irregularities during theformation of the recess and an effect during the formation of the metallayer), and the flatness of the metal layer is not easily degraded.Consequently, the depth of the recess provided in the first resininsulating layer can be easily made uniform, and the adhesiveness to asemiconductor device can be easily ensured. When a semiconductor deviceis accommodated in the recess, the tilt of the semiconductor device canbe prevented. Accordingly, when via holes connected to pads of theaccommodated semiconductor device are formed in the second resininsulating layer, via holes having a desired shape can be formed. Whenthe metal layer is substantially planarized, the electrode pads disposedon the surface of the semiconductor device are also substantiallyplanarized and thus connectivity in the via holes can be easily ensured.

Furthermore, the side faces of the recess for accommodating asemiconductor device may have a tapered shape. In such a case, even whenthe semiconductor device accommodated in the recess is subjected tostress (for example, thermal stress or external stress) in the lateraldirection, the stress can be relieved.

In addition, the phenomenon in which an adhesive used for fixing thesemiconductor device is diffused along the side faces of the recess doesnot occur, and the adhesiveness of the semiconductor device to thebottom of the recess is not easily decreased.

In the above embodiment, a columnar electrode or an intermediate layeris preferably provided on a pad of the semiconductor device.Accordingly, electrical connection between the pad of the semiconductordevice and a via hole can be easily established.

Pads of a semiconductor device are commonly formed of aluminum or thelike. In particular, when the pads do not include an intermediate layerand are simply formed of aluminum or the like and via holes are formedin an interlayer insulating layer by photoetching, the resin easilyremains on the surface of the pads after exposure and development, andadhesion of a developer may change the color of the pads.

On the other hand, when via holes are formed by laser machining, padsformed of aluminum or the like may be burned out. When the laserirradiation is performed under conditions that do not result in suchburning, the resin may remain on the pads. Furthermore, whenpost-processes (such as a step of immersing in an acid, an oxidant, oran etchant, a step of various types of annealing, and other processes)are performed, the color of the pads of the semiconductor device may bechanged or the pads may be dissolved. The pads of the semiconductordevice are formed so as to have a diameter of about 40 μm, and via holesare formed so as to have a larger diameter. Accordingly, a misalignmentor the like may be easily generated, and a problem of, for example, aconnection failure between the pads and the via holes easily occurs.

On the other hand, when an intermediate layer formed of copper or thelike is provided on the pads of the semiconductor device, the problemduring the formation of the via holes is eliminated and solvents can beused. Accordingly, a resin can be prevented from remaining on the pads,and the change in the color of the pads and dissolution of the pads donot occur even after post-processes. Accordingly, electricalconnectivity and connection reliability between pads and via holes arenot easily degraded. Furthermore, when an intermediate layer having adiameter larger than that of a die pad of the semiconductor device isinterposed, the pads and the via holes can be reliably connected.

Furthermore, when an intermediate layer is provided, checking ofoperations and electrical testing of the semiconductor device can beeasily performed before the semiconductor device is embedded in theprinted circuit board or accommodated, or after the semiconductor deviceis accommodated. The reason for this is that, since the intermediatelayer having a diameter larger than that of the pads of thesemiconductor device is provided, a probe pin for testing can be easilycontacted with the intermediate layer. Consequently, whether or not theproduct has an acceptable quality can be determined in advance. This isadvantageous in view of productivity and reduction in costs.Furthermore, for example, removal of pads and the formation of scratchesthereon due to contact with the probe do not easily occur. Accordingly,by forming the intermediate layer on the pads of the semiconductordevice, the semiconductor device can be suitably embedded andaccommodated in the printed circuit board.

A multilayered printed circuit board according to an embodiment of thepresent invention includes a semiconductor device, a first resininsulating layer accommodating the semiconductor device, a second resininsulating layer provided on the first resin insulating layer, aconductor circuit provided on the second resin insulating layer, and viaholes for electrically connecting the semiconductor device to theconductor circuit, wherein the semiconductor device is accommodated in arecess provided in the first resin insulating layer, a metal layer forplacing the semiconductor device is provided on the bottom face of therecess, and the wall surfaces of the recess are exposed.

In this embodiment, a space formed by the wall surfaces of the recessand the side faces of the semiconductor device is preferably filled witha resin layer. When the space is filled with a resin, the semiconductordevice can be stably disposed, and connectivity and reliability of thesemiconductor device can be easily ensured.

In addition, preferably, the space formed by the wall surfaces of therecess and the side faces of the semiconductor device is filled with aresin insulating layer, and the resin insulating layer is integratedwith the semiconductor device. In this case, the resin insulating layerin which via holes are formed and the resin insulating layer filling thespace formed by the wall surfaces of the recess and the side faces ofthe semiconductor device are composed of the same material. Accordingly,the generation of thermal stress due to, for example, the difference inthe thermal expansion coefficient between materials can be suppressed,and the semiconductor device can be stably disposed. Thus, connectivityand reliability of the semiconductor device can be easily ensured.

The side faces of the recess provided in the substrate may form atapered shape diverging from the bottom face upwards.

A columnar electrode or an intermediate layer may be provided on a padof the semiconductor device, and the pad of the semiconductor device maybe electrically connected to the via hole through the columnar electrodeor the intermediate layer.

A multilayered printed circuit board according to an embodiment of thepresent invention includes a semiconductor device, a first resininsulating layer accommodating the semiconductor device, a second resininsulating layer provided on the first resin insulating layer, aconductor circuit provided on the second resin insulating layer, and viaholes for electrically connecting the semiconductor device to theconductor circuit, wherein the semiconductor device is accommodated in arecess provided in the first resin insulating layer, a metal layer forplacing the semiconductor device is provided on the bottom face of therecess, and openings constituting the via holes are filled with aconductive substance.

In this embodiment, since the via holes are so-called filled vias,electrical characteristics when the via holes are connected to thesemiconductor device can be easily stabilized. It is believed thatconnectivity can be easily stabilized accordingly. Furthermore, when aninsulating layer or a conductor layer is provided as an upper layer ofthe via holes, irregularities or the like are not easily formed andelectrical connectivity can be easily ensured. Examples of theconductive substance include a plated metal and conductive paste.

The via holes preferably have a concave shape, viewed from the side.That is, the via holes preferably have a shape that is concave towardthe inside in the thickness direction. Accordingly, since a resininsulating layer is fitted with the via holes, it is believed that asatisfactory bondability of the via holes can be easily realized.

Solder pads are preferably provided above the semiconductor device. Inthis case, the distance between the solder pads and the semiconductordevice can be easily minimized, and satisfactory electricalcharacteristics can be easily obtained.

In this embodiment, preferably, the multilayered printed circuit boardfurther includes at least one resin insulating layer laminated on thesecond resin insulating layer, and via holes for connecting to theconductor circuit. Accordingly, the layout of wiring can be furtherextended. For example, the positions of the semiconductor device andexternal connections can be shifted. Thus, it is believed thatconnectivity and reliability can be easily obtained.

Furthermore, preferably, a columnar electrode or an intermediate layeris provided on a pad of the semiconductor device, and the pad iselectrically connected to the via hole through the columnar electrode orthe intermediate layer.

A multilayered printed circuit board according to an embodiment of thepresent invention includes a semiconductor device, a first resininsulating layer accommodating the semiconductor device, a second resininsulating layer provided on the first resin insulating layer, aconductor circuit provided on the second resin insulating layer, and viaholes for electrically connecting the semiconductor device to theconductor circuit, wherein the side faces of the recess form a taperedshape diverging from the bottom face upwards.

In this embodiment, regarding the tapered shape of the recess, among theangles formed by a side face and the bottom face of the recess, thesmaller angle is preferably in the range of at least 60 degrees and lessthan 90 degrees. In such a case, stress applied on the side face of thesemiconductor device can be relieved, thereby suppressing thedisplacement of the semiconductor device.

The wall surfaces of the recess are preferably exposed. Accordingly, theshape of the recess can be stabilized, and a space for accommodating thesemiconductor device can be ensured.

A space formed by the wall surfaces of the recess and the side faces ofthe semiconductor device is preferably filled with a resin layer. Whenthe space is filled with a resin, the semiconductor device can be stablydisposed. Accordingly, connectivity and reliability of the semiconductordevice can be easily ensured.

Furthermore, preferably, a space formed by the wall surfaces of therecess and the side faces of the semiconductor device is filled with aresin insulating layer, and the resin insulating layer is integratedwith the semiconductor device. In this case, the resin insulating layerin which via holes are formed and the resin insulating layer filling thespace formed by the wall surfaces of the recess and the side faces ofthe semiconductor device are composed of the same material. Accordingly,the generation of thermal stress due to, for example, the difference inthe thermal expansion coefficient between materials can be suppressed,and the semiconductor device can be stably disposed. Thus, connectivityand reliability of the semiconductor device can be easily ensured.

According to a method for manufacturing a multilayered printed circuitboard according to an embodiment of the present invention, in a methodfor manufacturing a multilayered printed circuit board wherein asemiconductor device is accommodated and fixed in a first resininsulating layer, a second resin insulating layer and a conductorcircuit are provided on the first resin insulating layer, and thesemiconductor device is electrically connected to the conductor circuitthrough via holes, the method includes the steps of:

forming a first insulating resin substrate by forming on a first surfaceof the first resin insulating layer at least a conductor circuit and ametal layer having a predetermined area corresponding to the dimensionsof the semiconductor device to be accommodated, forming on a secondsurface of the first resin insulating layer at least a conductor circuitand an area that does not have the conductor circuit thereon, the areahaving a predetermined area corresponding the dimensions of thesemiconductor device at a position facing the metal layer, and formingvia holes for electrically connecting the conductor circuit on the firstsurface to the conductor circuit on the second surface;

bonding a second insulating resin substrate prepared by applying acopper foil on a first surface of a third resin insulating layer ontothe first surface of the first insulating resin substrate under pressureto integrate the substrates;

forming a conductor circuit on the first surface of the secondinsulating resin substrate and forming via holes for electricallyconnecting the conductor circuit formed on the first surface of thesecond insulating resin substrate to the conductor circuit formed on thefirst surface of the first insulating resin substrate;

forming, on the area of the first insulating resin substrate that doesnot have the conductor circuit thereon, a recess extending from thesurface of the first resin insulating layer to the surface of the metallayer so as to expose the surface of the metal layer;

accommodating a semiconductor device in the recess, and bonding andfixing the semiconductor device on the surface of the metal layerexposed in the recess, with an adhesive therebetween; and

covering the semiconductor device, forming the second resin insulatinglayer and a conductor circuit thereon, and then forming via holes forelectrically connecting the semiconductor device and the conductorcircuit.

In the embodiment of the above method, the recess is preferably formedby laser irradiation.

The side faces of the recess preferably form a tapered shape divergingfrom the bottom face upwards.

When a columnar electrode or an intermediate layer is formed on a pad ofthe semiconductor device in advance, the pad can be electricallyconnected to the via hole through the columnar electrode or theintermediate layer.

According to this embodiment, by forming the metal layer on the bottomface of the recess provided on the first resin insulating layer, thedepth of the recess can be easily made uniform. When the recessparticularly has a rectangular cross section, the depth of the recessaround the four corners can also be easily made uniform.

Furthermore, since the metal layer is substantially planarized,electrical connectivity and connection reliability can be further easilyensured. Since the metal layer is formed in the resin insulating layer,warpage due to thermal stress, external stress, or the like is noteasily generated. Consequently, for example, since connection failurebetween connection pads of the semiconductor device and a conductorcircuit including via holes does not easily occur, electricalconnectivity and connection reliability can be easily ensured.

A multilayered printed circuit board of the present invention will nowbe described in detail with reference to the attached drawings.

Examples of a resin insulating layer for accommodating a semiconductordevice that can be used in an embodiment of the present inventioninclude a hard laminated substrate selected from a glass-cloth epoxyresin substrate, a phenol resin substrate, a glass-clothbismaleimide-triazine resin substrate, a glass-cloth polyphenylene etherresin substrate, an aramid non-woven fabric epoxy resin substrate, anaramid non-woven fabric polyimide resin substrate, and the like. Theseare preferably fiber substrates such as a glass epoxy or a resinmaterial in which a prepreg or a core material is impregnated. Inaddition to these, substrates that are generally used for printedcircuit boards can be used. For example, a double-sided or single-sidedcopper clad laminate, a resin plate that does not have a metal film, aresin film, or a composite material of these can also be used.

The thickness of the resin substrate is preferably in the range of about20 to 350 μm. When the thickness is within the above range, theinsulating property of an interlayer insulating layer can be easilyensured, via holes for interlayer connection can be easily formed, andelectrical connectivity is not easily degraded.

In the embodiment of the present invention, copper is preferably used asthe metal layer used for forming a conductor circuit and the metal layerformed on the bottom face of the recess provided in the resin insulatinglayer because copper can be easily processed by etching. Accordingly,the size of the metal layer can be freely changed. In addition, whenelectrical connectivity is provided to the metal layer formed on thebottom face of the recess, a copper metal layer has excellent electricalcharacteristics.

The thickness of a copper foil used for forming a conductor circuit ispreferably in the range of about 5 to 20 μm. In the case where thethickness of the copper foil is within the above range, when openingsfor forming via holes are made in the insulating resin substrate bylaser machining as described below, the copper foil disposed at theperiphery of the openings is not deformed and the conductor circuit canbe easily formed. Furthermore, a conductor circuit pattern having a fineline-width can be easily formed by etching.

The thickness of the copper foil used in the embodiment of the presentinvention may be adjusted by a half-etching process. In such a case, thecopper foil applied on the resin insulating layer preferably has athickness larger than the above numerical values, and the thickness ofthe copper foil is preferably adjusted to about 5 to 20 μm afteretching.

In a double-sided copper clad laminate, the thickness of the copper foilis preferably within the above range, but the thickness may be differentbetween both sides. Thus, for example, the strength of the laminate isensured so that a post-process may be performed smoothly.

A copper foil serving as the metal layer provided on the bottom face ofthe recess preferably has a thickness of about 5 to 20 μm. When thethickness of the copper foil is within the above range, the copper foilis not easily pierced during a cavity processing. Therefore, the effectof forming the metal layer is not cancelled out. Furthermore, the metallayer can be easily formed by etching.

Instead of copper, a metal such as nickel, iron, or cobalt may be usedfor the metal layer provided on the bottom face of the recess.Alternatively, an alloy containing at least one of these metals may alsobe used.

As regards the insulating resin substrate and the copper foil, inparticular, a single-sided or double-sided copper clad laminate producedby laminating a copper foil on a B-stage prepreg in which a glass clothis impregnated with an epoxy resin and then pressing the laminate underheating is preferably used. In such a copper clad laminate, thepositions of a wiring pattern and via holes are not shifted duringhandling of the laminate after the copper foil is etched, and thus theaccuracy of the positions is excellent.

In the embodiment of the present invention, the recess for accommodatinga semiconductor device, the recess being provided in the resininsulating layer, can be formed by laser machining, a counterboringprocess, or punching. In particular, the recess is preferably formed bylaser machining.

When the recess is formed by laser machining, the uniformity of thedepth of the recess can be easily achieved and, in particular, theuniformity of the depth to the metal layer is excellent compared withthe counterboring process. Consequently, for example, when asemiconductor device is accommodated in the recess, a problem of a tiltof the semiconductor device can be suppressed. Furthermore, a processingto obtain a tapered shape described below can be accurately performed.

When the recess is formed by the counterboring process, since the metallayer provided on the bottom face of the recess functions as a stopper,the depth of the recess can be made uniform.

The depth of the recess is determined in accordance with the thicknessof the semiconductor device to be accommodated therein and the thicknessof the columnar electrode or the intermediate layer that may be formedon a connection pad of the semiconductor device. Since a metal layerthat is substantially flat is formed on the entire surface of the bottomof the recess, an adhesive layer provided between the semiconductordevice and the resin insulating layer can easily have a uniformthickness.

As a result, the adhesiveness between the semiconductor device and theresin insulating layer can be uniformly maintained. Therefore, even whena reliability test is repeatedly performed under a heat-cycle condition,the adhesiveness can be easily ensured.

In a related art, a recess for accommodating a semiconductor device isformed in an insulating substrate composed of only a resin insulatinglayer by, for example, machining. FIGS. 10A to 10D show an example ofsteps of manufacturing such a printed circuit board. As shown in FIG.10A, first, an insulating substrate 100 composed of a resin insulatinglayer is prepared. As shown in FIG. 10B, a recess 102 is then formed inthe insulating substrate 100 by machining (such as punching or acounterboring process). As shown in FIGS. 10C and 10D, an adhesive layer104 is formed on the bottom of the recess 102 and a semiconductor device106 is then accommodated. Accordingly, a printed circuit board in whichthe semiconductor device 106 is accommodated in the insulating substrate100 is produced (see FIG. 11).

In this case, the insulating material includes only a resin. Forexample, an insulating layer prepared by laminating sublayers composedof a material in which a core material is impregnated with a resin canbe used. In such a case, when the above-described machining isperformed, the recess may not be easily flat. That is, when the recessis formed by machining, irregularities are formed because of thedifference in the depth of the recess, the condition of the resin (sincethe core material is woven in the resin, the presence or the absence ofthe core material depends on positions), or the like. When thesemiconductor device is accommodated in the recess, the presence of theirregularities causes a tilt of the semiconductor device. Accordingly,it may be difficult to ensure the connectivity between the electrodepads and via holes. In addition, when a resin not including a corematerial or the like is used for an insulating layer in which via holesare formed, it may be difficult to ensure the connection by the viaholes.

Accordingly, in the present invention, side faces of the recess foraccommodating a semiconductor device preferably form a tapered shapediverging from the bottom face upwards. According to such a structure,even when the semiconductor device accommodated in the recess issubjected to stress (for example, thermal stress or external stress) inthe lateral direction, the stress can be relieved. Furthermore, thisstructure can suppress the phenomenon in which an adhesive, which isapplied on the bottom face of the semiconductor device in order to fixthe semiconductor device, flows along the side faces of the recess bycapillary action. Consequently, the adhesiveness of the semiconductordevice to the bottom of the recess can be easily ensured.

In the embodiment of the present invention, as shown in FIG. 1, theangle of the above taper is defined as an exterior angle formed by theside face and the bottom face of the recess. The taper angle ispreferably at least 60 degrees and less than 90 degrees, and morepreferably in the range of 60 to 85 degrees. At an angle within theabove range, stress applied on the side face of the semiconductor devicecan be relieved, thereby suppressing the displacement of thesemiconductor device. Therefore, during a reliability test, connectionfailure at via holes does not easily occur in the early stage.

In the embodiment of the present invention, two insulating resinsubstrates described above are used as the resin insulating layer foraccommodating a semiconductor device. More specifically, the resininsulating layer includes a first insulating resin substrate in which ametal layer having dimensions corresponding to the dimensions of thesemiconductor device is provided on one surface and a second insulatingresin substrate that is laminated on the surface of the first insulatingresin substrate, the surface having the metal layer. A recess foraccommodating the semiconductor device is formed by laser machining onthe other surface of the first insulating resin substrate so as to reachthe metal layer. Thus, a substrate for accommodating a semiconductor inwhich the metal layer is exposed from the recess is formed. The exposedmetal layer is installed in advance and has a substantially flatsurface.

In another embodiment, a first insulating resin substrate in which ametal layer having dimensions corresponding to the dimensions of thesemiconductor device is provided on one surface and a second insulatingresin substrate in which an opening is provided in advance at an areacorresponding to the metal layer may be laminated to form a recess inwhich one side of the opening is closed. Thus, a substrate foraccommodating a semiconductor in which the metal layer is exposed fromthe recess may be formed.

In such an embodiment, each of the first insulating resin substrate andthe second insulating resin substrate preferably has a thickness ofabout 20 to 250 μm. When the thickness is within this range, theinsulating property of an interlayer insulating layer can be easilyensured, via holes for interlayer connection can be easily formed, andelectrical connectivity can be easily ensured.

Each of the insulating resin substrates used may be a resin substrateincluding a single layer. Alternatively, the insulating resin substratemay be a multilayered resin substrate including two or more layers.

After the semiconductor device is embedded in the recess of thesubstrate for accommodating a semiconductor, an interlayer resininsulating layer is formed on at least one surface of the substrate foraccommodating a semiconductor. Subsequently, a conductor circuitincluding via holes for establishing the electrical connection to thesemiconductor device is formed on the interlayer resin insulating layer.Furthermore, other interlayer resin insulating layers and conductorcircuits are then alternately laminated, thereby manufacturing themultilayered printed circuit board of the present invention.

As regards the semiconductor device embedded in the recess of thesubstrate for accommodating a semiconductor, either a semiconductordevice in which columnar electrodes are provided in advance onconnection pads of the device or a semiconductor device including anintermediate layer that covers connection pads can be used. Preferably,such a semiconductor device is electrically connected to the via holesprovided in the interlayer resin insulating layer, with the columnarelectrodes or the intermediate layer therebetween.

Methods for manufacturing (1) a semiconductor device having columnarelectrodes and (2) a semiconductor device having an intermediate layerwill be described below.

(1) Method for Manufacturing Semiconductor Device Having ColumnarElectrodes

A semiconductor device that has columnar electrodes and that is used inan embodiment of the present invention means a semiconductor devicehaving columnar electrodes or rewiring.

As shown in FIG. 2, connection pads 2 composed of aluminum or the likeare formed on a semiconductor device 1 (silicon substrate), which is inthe form of a wafer. A protective layer (passivation film) 3 is formedon areas except for the central part of each connection pad 2. In thisstate, the surface of the connection pads 2 is exposed at their centralpart that is not covered with the protective layer 3.

A metal underlayer 4 is then formed on the entire surface of thesemiconductor device 1. Chromium, copper, nickel, or the like can beused for the metal underlayer 4.

A plating resist layer composed of a liquid resist is then formed on themetal underlayer 4. Openings are formed in areas of the plating resistlayer, the areas corresponding to the connection pads 2 of thesemiconductor device 1.

Subsequently, electrolytic plating is performed using the metalunderlayer 4 as a plating current path. Accordingly, columnar electrodes5 are formed on the metal underlayer 4 disposed in the openings of theplating resist layer. The plating resist layer is then removed, and theunnecessary parts of the metal underlayer 4 are removed by etching usingthe columnar electrodes 5 as a mask. Accordingly, the metal underlayer 4remains only under the columnar electrodes 5.

Furthermore, a sealing film 6 composed of an epoxy resin, a polyimide,or the like is formed on the surface semiconductor device 1. In thisstate, when the top surface of the columnar electrodes 5 is covered withthe sealing film 6, the surface is appropriately polished so as toexpose the top surface of the columnar electrodes 5. Next, a dicingprocess is performed to produce semiconductor chips (semiconductordevices having columnar electrodes).

(2) Method for Manufacturing Semiconductor Device Having IntermediateLayer

The intermediate layer used in an embodiment of the present inventionmeans an intermediate layer for electrically connecting thesemiconductor device to via holes provided on the pads of thesemiconductor device.

As shown in FIG. 3, a conductive metal layer 12 (first thin-film layer)is formed on the entire surface of a semiconductor device 10 to beinstalled by vapor deposition, sputtering, or the like. The metal ispreferably tin, chromium, titanium, nickel, zinc, cobalt, gold, copper,or the like. The first thin-film layer 12 is preferably formed so as tohave a thickness in the range of about 0.001 to 2.0 μm. When thethickness is within this range, a metal layer having a uniform thicknessover the entire surface can be easily formed, thus suppressingvariations in the film thickness. When the first thin-film layer 12 iscomposed of chromium, the thickness is preferably about 0.1 μm.

A connection pad 14 is covered with the first thin-film layer 12 toincrease the adhesiveness at the interface between an intermediate layer20 and the connection pad 14 of the semiconductor device 10.Furthermore, by covering the connection pad 14 of the semiconductordevice 10 with the above metal, intrusion of moisture into the interfacecan be prevented to prevent dissolution or corrosion of the connectionpad 14. Accordingly, the reliability is not easily degraded.

Any one of chromium, nickel, and titanium is preferably used as themetal of the first thin-film layer 12 because satisfactory adhesivenessbetween the connection pad 14 and the first thin-film layer 12 can beachieved and the intrusion of moisture into the interface can be easilyprevented.

A second thin-film layer 17 is then formed on the first thin-film layer12 by sputtering, vapor deposition, or electroless plating. Nickel,copper, gold, silver, or the like is used for the second thin-film layer17. From the standpoints of electrical characteristics, economicalefficiency, and the fact that a thick layer formed in a subsequent stepis primarily composed of copper, preferably, the second thin-film layer17 is also composed of copper.

The reason for the formation of the second thin-film layer 17 is that itis difficult to obtain a plating lead used for electrolytic plating forforming the thick layer described below when only the first thin-filmlayer 12 is provided. The second thin-film layer 17 is used as theplating lead for forming the thick layer.

The thickness of the second thin-film layer 17 is preferably in therange of about 0.01 to 5.0 μm. When the thickness is within this range,the second thin-film layer 17 can function as the plating lead. Inaddition, during etching, the phenomenon in which the lower firstthin-film layer 12 is excessively etched to form a clearance can besuppressed, and moisture is not easily intruded. Accordingly, thereliability can be easily ensured.

A metal thick layer is formed on the second thin-film layer 17 byelectroless or electrolytic plating. Examples of the metal used for thethick layer include nickel, copper, gold, silver, zinc, and iron. Fromthe standpoints of electrical characteristics, economical efficiency,the strength as an intermediate layer, the resistance in the structure,and the fact that a conductor layer of a build-up wiring layer, which isformed in a subsequent step, is primarily composed of copper, the thicklayer is preferably formed by electrolytic copper plating.

The thickness of a thick electrolytic copper plating layer (thick layer)18 is preferably in the range of about 1 to 20 μm. When the thickness iswithin this range, connection reliability with a via hole provided inthe upper layer is not easily decreased. In addition, since undercut isnot easily formed during etching, the generation of a clearance betweenthe intermediate layer to be formed and the via hole can be suppressed.Alternatively, in some cases, the thick layer 18 may be formed directlyon the first thin-film layer by plating. The thick layer 18 may beformed by laminating a plurality of layers.

An etching resist is then formed thereon. Exposure and development arethen performed to expose the metal layer disposed in areas other thanthe intermediate layer. The exposed metal parts are then etched.Accordingly, the intermediate layer 20 including the first thin-filmlayer 12, the second thin-film layer 17, and the thick layer 18 isformed on the connection pad 14 of the semiconductor device.

In addition to the above-described method, the intermediate layer may beformed as follows. After a semiconductor device is installed in a recessof a substrate, the intermediate layer may be formed. Alternatively, ametal film is formed on a semiconductor device and a core substrate, anda dry film resist is then formed on the metal film. Subsequently, a partof the dry film resist disposed in areas corresponding to theintermediate layer is then removed. The thick layer is then formed byelectrolytic plating. The remaining resist is removed, and the exposedmetal film is then removed with an etchant. Thus, the intermediate layermay be formed on die pads of the semiconductor device.

Next, an example of a method for manufacturing a multilayered printedcircuit board of the present invention will be described morespecifically.

A. Preparation of Substrate for Accommodating Semiconductor Device

In producing a multilayered printed circuit board according to thepresent invention, a substrate prepared by laminating a first insulatingresin substrate and a second insulating resin substrate in which acopper foil is applied on at least one side of the insulating resinsubstrate is used as a substrate for accommodating a semiconductordevice, the substrate constituting the multilayered printed circuitboard.

(1) The first insulating resin substrate can be formed from, forexample, a double-sided copper clad laminate. A surface of such adouble-sided copper clad laminate is irradiated with a laser beam toform openings for forming via holes. The openings penetrate through thesurface of one of the copper foils of the first insulating resinsubstrate and the resin insulating layer and reach the other copper foil(or a conductor circuit pattern).

The laser irradiation is performed with a pulse oscillation-type carbondioxide gas laser drilling machine. Regarding the processing conditions,the pulse energy is preferably in the range of about 0.5 to 100 mJ, thepulse width is preferably in the range of about 1 to 100 μs, the pulseinterval is preferably in the range of about 0.5 ms or more, thefrequency is preferably in the range of about 2,000 to 3,000 Hz, and thenumber of shots is preferably in the range of 1 to 5.

The diameter of the openings for forming via holes formed under theabove conditions is preferably in the range of about 50 to 250 μm.

To form the openings for forming via holes in a copper clad laminate bylaser irradiation, either a direct laser method in which laserirradiation is performed so that the openings are simultaneously formedin a copper foil and an insulating resin substrate or a conformal methodin which a part of a copper foil corresponding to the openings forforming via holes is removed by etching in advance and an insulatingresin substrate is then irradiated with a beam may be used.

(2) In order to remove resin residues remaining in the openings formedin the above step, a desmear process is preferably performed.

This desmear process is performed by a wet process such as a treatmentwith a chemical of an acid or an oxidant (e.g., chromic acid orpermanganic acid) or a dry process such as an oxygen plasma dischargetreatment, a corona discharge treatment, an ultraviolet laser treatment,or an excimer laser treatment.

The method of the desmear process is selected in accordance with theexpected amount of residual smear that depends on the type and thethickness of insulating resin substrate used, the diameter of the viaholes, laser conditions, and the like.

(3) Electrolytic copper plating is performed using the copper foil as aplating lead on the surface of the copper foil of the substrate that hasbeen subjected to the desmear process. Accordingly, the openings arecompletely filled with copper formed by electrolytic plating to formfilled vias.

Optionally, after the electrolytic copper plating, a part of the platedcopper protruding from the top of the opening for forming the via holesof the substrate may be removed by belt sanding, buffing, etching, orthe like to planarize the surface.

(4) A resist layer is then formed on either side of the first insulatingresin substrate, and exposure and development are then performed.Subsequently, copper disposed on areas where the resist layer is notformed is etched with an etchant containing cupric chloride or the like,and the resist layer is then removed. Accordingly, a conductor circuitincluding via hole lands, a mark for positioning, and the like areformed on one surface of the first insulating resin substrate. A metallayer having dimensions corresponding to the dimensions of asemiconductor device, a conductor circuit including via hole lands, amark for positioning, and the like are formed on the other surface ofthe first insulating resin substrate.

(5) A second insulating resin substrate is laminated on a surface of thefirst insulating resin substrate, the surface having the metal layerthereon.

For example, the second insulating resin substrate is prepared bylaminating a copper foil on a prepreg, which is as an adhesive layer.The second insulating resin substrate is laminated on one surface of thefirst insulating resin substrate by thermocompression bonding to form alaminate.

(6) Laser irradiation is performed onto a surface of the firstinsulating resin substrate constituting the laminate, the surface havingthe metal layer, as in step (1) above. Accordingly, openings for formingvia holes are formed. The openings penetrate through the surface of thecopper foil of the second insulating resin substrate and the resin layerand reach the conductor circuit that is formed on the first insulatingresin substrate and that includes the via hole lands.

Regarding the processing conditions for the openings for forming viaholes, the pulse energy is preferably in the range of about 0.5 to 100mJ, the pulse width is preferably in the range of about 1 to 100 μs, thepulse interval is preferably in the range of about 0.5 ms or more, thefrequency is preferably in the range of about 2,000 to 3,000 Hz, and thenumber of shots is preferably in the range of 1 to 10.

The diameter of the openings for forming via holes formed under theabove processing conditions is preferably in the range of about 50 to150 μm. When the diameter of the openings is within this range,interlayer connectivity can be easily ensured and a high-density wiringcan be easily achieved.

(7) In order to remove resin residues remaining in the openings forforming via holes formed in step (6), a desmear process is performed asin step (2).

(8) The surface of the first insulating resin substrate is covered witha protective film, and electrolytic copper plating is then performedusing the copper foil as a plating lead on the surface of the copperfoil of the substrate that has been subjected to the desmear process.Accordingly, the openings are completely filled with copper formed byelectrolytic plating to form filled vias.

Optionally, after the electrolytic copper plating, a part of the platedcopper protruding from the top of the opening for forming the via holesof the substrate may be removed by belt sanding, buffing, etching, orthe like to planarize the surface.

Alternatively, electroless plating may be performed in advance, andelectrolytic plating may then be performed. In such a case, a metal suchas copper, nickel, or silver may be used for the film formed by theelectroless plating.

(9) A resist layer is formed on the copper film formed by electrolyticplating. The resist layer may be formed by applying a liquid resist andthen curing the resist or applying a dry film resist. A mask including acircuit pattern is disposed on the resist layer. Exposure anddevelopment are then performed to form an etching resist layer. Themetal layer disposed at areas where the etching resist layer is notformed is etched to form a conductor circuit including via hole lands.The protective film applied in step (8) is then removed.

The etchant used in the above etching is preferably at least one aqueoussolution selected from aqueous solutions of sulfuric acid/hydrogenperoxide, persulfates, cupric chloride, and ferric chloride.

In order to easily form a fine pattern, as a preliminary treatment forforming the conductor circuit by etching the copper foil, the thicknessof the copper foil may be adjusted in advance by etching the entiresurface thereof.

The via hole lands, which are a part of the conductor circuit, arepreferably formed so that the inner diameter of the via hole lands issubstantially the same as the diameter of the via holes, or the outerdiameter thereof is larger than the diameter of the via holes. The landdiameter is preferably in the range of about 75 to 350 μm.

(10) Subsequently, an opening penetrating through the resin layer andreaching the surface of the metal layer is formed by, for example, lasermachining on a surface area (area for accommodating a semiconductordevice) of the first insulating resin substrate, the surface area beingdisposed at the side opposite the metal layer. Accordingly, a recess isformed so that the surface of the metal layer is exposed from theopening, thus forming the substrate for accommodating a semiconductordevice. As required, the recess on which the metal layer is exposed maybe formed by forming a resist layer, and then performing an etchingprocess.

For example, an opening penetrating through the surface of the firstinsulating resin substrate and the resin layer and reaching the surfaceof the metal layer is formed on the laminate including the firstinsulating resin substrate and the second insulating resin substrate bylaser irradiation with a pulse oscillation-type carbon dioxide gas laserdrilling machine. Thus, a recess for accommodating or installing asemiconductor device is formed.

Regarding the processing conditions for forming the recess thataccommodates a semiconductor device, the pulse energy is preferably inthe range of about 0.5 to 100 mJ, the pulse width is preferably in therange of about 1 to 100 μs, the pulse interval is preferably in therange of about 0.5 ms or more, the frequency is preferably in the rangeof about 2,000 to 3,000 Hz, and the number of shots is preferably in therange of 1 to 10.

The recess for installing a semiconductor device is formed by such lasermachining, and the metal layer (in this case, copper foil) is exposed onthe bottom face of the recess. In this case, the metal layer has a shinysurface and a substantially flat surface. According to need, the surfaceof the metal layer may be roughened to some degree by a blackeningtreatment or the like. Thereby, the adhesiveness to the adhesive layermay be ensured.

B. Accommodation and Embedding of Semiconductor Device

(11) A semiconductor device is embedded in the substrate foraccommodating a semiconductor device produced in steps (1) to (10) ofprocess A above.

As described above, either a semiconductor device in which columnarelectrodes are provided in advance on connection pads or a semiconductordevice including an intermediate layer that covers connection pads canbe used as the semiconductor device to be embedded. Here, a descriptionwill be made of the case where the latter semiconductor device is used.

This intermediate layer is provided in order to directly connect thepads of the semiconductor device to the conductor circuit including viaholes of the printed circuit board. The intermediate layer is formed byforming a thin-film layer on die pads, and further forming a thick layeron the thin-film layer. The intermediate layer preferably includes atleast two metal layers.

The dimensions of the intermediate layer are preferably larger than thedimensions of the die pads of the semiconductor device. In such a case,positional alignment with the die pads can be easily performed.Consequently, electrical connectivity with the die pads can be improved,and processes for forming via holes by laser irradiation andphoto-etching can be performed without damaging the die pads.Accordingly, embedding and accommodation of the semiconductor device inthe printed circuit board, and electrical connection between thesemiconductor device and the printed circuit board can be reliablyperformed.

Furthermore, a metal layer constituting a conductor circuit of theprinted circuit board can be directly formed on the intermediate layer.

In addition to the above-described method, the intermediate layer can bemanufactured by the following method. A metal layer is formed on anentire surface of the semiconductor device, the surface having theconnection pads, or a metal layer is formed on the substrate foraccommodating a semiconductor device in which the semiconductor deviceis embedded. A dry film resist is formed on the metal layer, and a partof the resist disposed at areas corresponding to the intermediate layeris then removed. Subsequently, a thick layer is formed by electrolyticplating. The remaining resist is removed, and the exposed metal layer isthen removed with an etchant. Thus, the intermediate layer can be formedon the connection pads of the semiconductor device.

(12) A resin insulating layer is formed on the substrate accommodatingand installing the semiconductor device, and steps the same as steps (1)to (4) of process A are then performed. Accordingly, via holes that areelectrically connected to the intermediate layer formed on connectionpads of the installed semiconductor device, via holes that areelectrically connected to the conductor circuit including via holes andformed on the substrate for accommodating the semiconductor device, andthe external conductor circuit can be formed. In this step, a mattetreatment may be performed on the conductor circuit and the metal layeron the substrate. Techniques for forming a matte surface by rougheningthe surface of the metal layer, such as etching, plating, anoxidation-reduction treatment, and a blackening treatment, can be usedfor the matte treatment.

Furthermore, a resin insulating layer and a copper foil are laminated,and steps the same as steps (1) to (4) of process A are repeated.Accordingly, a printed circuit board including further laminated layerscan be produced.

In the above method, resin insulating layers are laminated bysequentially laminating a resin insulating layer. Alternatively,according to need, two or more circuit boards each including a singleresin insulating layer may be laminated and then subjected tothermocompression bonding at one time. Thus, resin insulating layers maybe laminated to form a multilayered printed circuit board.

(13) Next, a solder resist layer is formed on each outer surface of theoutermost circuit boards. In this step, a solder resist composition isapplied on the entire outer surface of the circuit boards, and theresist film is then dried. A photomask film having a pattern of openingsof solder pads is disposed on the resist film, and exposure anddevelopment are then performed. Accordingly, solder-pad openings inwhich conductive pad areas located directly on the via holes of theconductor circuit are exposed are formed. Alternatively, the openingsmay be formed by applying a dry film resist serving as the solder resistlayer, and exposing and developing the resist or by machining the resistwith a laser.

A corrosion-resistant layer composed of, for example, a nickel/goldlayer is formed on the solder pads exposed on the areas where the masklayer is not formed. The thickness of the nickel layer is preferably inthe range of about 1 to 7 μm, and the thickness of the gold layer ispreferably in the range of about 0.01 to 0.1 μm.

Alternatively, a nickel/palladium/gold layer, a gold layer (singlelayer), a silver layer (single layer), or the like may be formed. Afterthe corrosion-resistant layer is formed, the mask layer is removed.Accordingly, a printed circuit board including solder pads having thecorrosion-resistant layer and solder pads that do not have thecorrosion-resistant layer is prepared.

(14) Solder is supplied to the solder pad areas exposed directly on thevia holes from the openings of the solder resist prepared in step (13).The solder is then melted and solidified to form a multilayered printedcircuit board having a solder layer thereon. Alternatively, solderbumps, conductive balls, or conductive pins may be bonded on the padareas, with a conductive adhesive or a solder layer therebetween.

In a solder transferring method, a solder foil is bonded on a prepreg,and the solder foil is then etched so that the solder remains in onlyareas corresponding to solder-resist openings to form a solder pattern.Thus, a solder carrier film is prepared. A flux is applied on thesolder-resist openings of a substrate. The solder carrier film is thenlaminated on the substrate so that the solder pattern is in contact withpads, and the solder is then transferred by heating.

On the other hand, in a printing method, a printing mask (metal mask) inwhich openings are provided at positions corresponding to pads isdisposed on a substrate. Solder paste is printed on the mask and is thenheated. For example, Sn/Ag solder, Sn/In solder, Sn/Zn solder, or Sn/Bisolder can be used as solder for forming such a solder layer.

Example 1 (1) Preparation of Substrate

First, a printed circuit board constituting a substrate foraccommodating a semiconductor device is prepared. This printed circuitboard includes a first insulating substrate 30 and a second insulatingsubstrate 40 and is formed by laminating these substrates. An example ofthe starting material of the printed circuit board is a double-sidedcopper clad laminate prepared by laminating a copper foil on a B-stageprepreg in which a glass cloth is impregnated with an epoxy resin, andthen pressing the laminate under heating.

A double-sided copper clad laminate is used as the first insulatingsubstrate 30. In the double-sided copper clad laminate, a copper foil 34having a thickness of 15 μm is bonded on the top face and the bottomface of a resin insulating layer 32 having a thickness of 100 μm. Thecopper foil 32 of the copper clad laminate may have a thickness of morethan 15 μm. In such a case, the thickness of the copper foil may beadjusted to 15 μm by etching (see FIG. 4A).

A metal layer, which constitutes a bottom face of a recess forinstalling a semiconductor device, a conductor circuit, and the like areformed by photolithography including a resist formation and an etchingprocess on a surface of the first insulating substrate 30, the surfaceto be in contact with the second insulating substrate 40, as describedbelow. A mark for positioning during laser perforation and the like mayalso be formed according to need.

(2) Formation of Openings for Forming Via Holes

A surface of one of the copper foils of the first insulating substrate30 is irradiated with a carbon dioxide gas laser to form openings 36 forforming via holes. The openings 36 penetrate through the copper foil 34and the resin insulating layer 32 and reach a surface of the othercopper foil 34 (see FIG. 4B). Furthermore, a desmear process is thenperformed for the openings 36 using a solution of permanganic acid.

In this example, the openings 36 for forming via holes are formed asfollows with a high-peak short-pulse oscillation-type carbon dioxide gaslaser drilling machine manufactured by Hitachi Via Engineering, Ltd. Alaser beam is directly irradiated onto the copper foil 34 provided onthe resin insulating layer (glass-cloth epoxy resin substrate) having asubstrate thickness of 60 μm under the following irradiation conditions.The openings 36 for forming via holes each have a diameter of 75 μm andare formed at a rate of 100 openings/second.

(Irradiation Conditions)

Pulse energy: 75 mJ

Pulse width: 80 μs

Pulse interval: 0.7 ms

Frequency: 2,000 Hz

(3) Formation of Electrolytic Copper Plating Film

After the desmear process, electrolytic copper plating is performed onthe surface of the copper foil of the first insulating substrate 30 onwhich the openings 36 for forming via holes are provided using thecopper foil as a plating lead. The plating conditions are as follows.

[Electrolytic Plating Solution]

Sulfuric acid: 2.24 mol/L

Copper sulfate: 0.26 mol/L

Additive A (reaction accelerator): 11.0 mL/L

Additive B (reaction inhibitor): 10.0 mL/L

[Conditions for Electrolytic Plating]

Current density: 1 A/dm²

Time: 65 minutes

Temperature: 22° C.±2° C.

According to the above plating process, the formation of an electrolyticcopper plating film 38 in the openings is accelerated by the additive A.On the other hand, the additive B is mainly adhered to the copper foilpart, and the formation of the plated film is suppressed. When theopenings are filled with the electrolytic copper plating film and theheight thereof substantially becomes the same as that of the copperfoil, the additive B is adhered to the copper plating film and theformation of the plated film is suppressed as in the copper foil part.Accordingly, the openings are completely filled with the electrolyticcopper plating film, and the electrolytic copper plating film 38 exposedfrom the openings and the copper foil 34 substantially form a flatsurface (see FIG. 4C).

The thickness of a conductor layer composed of the copper foil 34 andthe electrolytic copper plating film 38 may be adjusted by etching. Thethickness of the conductor layer may be adjusted by a physical method,such as belt sanding or buffing, as required.

(4) Formation of Conductor Circuit, Filled Vias, and Metal Layer

After step (3), an etching resist layer (not shown) is formed on eachcopper foil 34 of the first insulating substrate 30 and the electrolyticcopper plating film 38 using a photosensitive dry film. That is, theetching resist layer is formed on each copper foil 34 disposed on thetop face and the bottom face of the first insulating substrate 30. Thethickness of each resist layer is in the range of 15 to 20 μm. Theresist layers are exposed using masks having a pattern of a conductorcircuit including lands of filled vias and a pattern of a metal layerhaving dimensions corresponding to the dimensions of a semiconductordevice, and then developed. Accordingly, areas that do not have theresist layer thereon are formed on the copper foils.

Subsequently, the electrolytic copper plating film 38 and the copperfoil 34 on the above areas that do not have the resist layer are removedby etching with an etchant composed of aqueous hydrogen peroxide andsulfuric acid.

The resist layers are then removed by an alkaline solution. Accordingly,conductor circuits 41 including lands of filled vias 39, and a metallayer 42 with which a semiconductor device is brought into contact areformed. A dummy pattern, an alignment mark, a product identificationcode, and the like may also be formed according to need.

Consequently, a circuit board in which the conductor circuit 41 isformed on each of the top face and the bottom face of the firstinsulating substrate 30 and which has filled vias 39 that electricallyconnected these conductor circuits 41, and the metal layer 42 foraccommodating a semiconductor device thereon is prepared.

As shown in FIG. 1, the metal layer 42 formed on the circuit board isprovided on the reverse face of the first insulating substrate, and thecopper foil part on the surface of the circuit board, the partcorresponding to the area where a recess for accommodating asemiconductor device is formed, is removed by etching (see FIG. 4D).

(5) Lamination of First Insulating Substrate and Second InsulatingSubstrate

As shown in FIG. 4E, a single-sided copper clad laminate is used as thesecond insulating substrate 40 laminated on the first insulatingsubstrate 30. In the single-sided copper clad laminate, a copper foil 44having a thickness of 15 μm is bonded on a surface of a resin insulatinglayer 43 having a thickness of 60 μm.

The second insulating substrate 40 is laminated on the first insulatingsubstrate 30 so that the surface that does not have the copper foil 44is in contact with the surface having the metal layer 42 of the firstinsulating substrate 30 (the metal layer 42 functions as a metal layerfor accommodating a semiconductor device thereon). The first insulatingsubstrate 30 is laminated on the second insulating substrate 40 bythermocompression bonding under the following conditions (see FIG. 4E).In this step, a treatment for forming a matte surface (for example, theformation of a roughened surface by etching) may be performed on theconductor circuit 41 and the metal layer 42.

(Conditions for Thermocompression)

Temperature: 180° C.

Pressure during pressing: 150 kgf/cm²

Time of compression bonding: 15 minutes

In this embodiment, each of the first insulating substrate 30 and thesecond insulating substrate 40 is composed of a single layer.Alternatively, each of these substrates may be composed of two or morelayers.

(6) Formation of Openings for Forming Via Holes

The surface of the copper foil 44 of the second insulating substrate 40is irradiated with a carbon dioxide gas laser to form openings 46 forforming via holes. The openings 46 penetrate through the copper foil 44,pass the resin insulating layer 43, and reach the surface of theconductor circuit 41 including via lands of the filled vias 39 providedon the first insulating substrate 30 (see FIG. 4F). Furthermore, adesmear process is then performed for the openings 46 using a solutionof permanganic acid.

In this example, in order to form the openings 46 for forming via holesin the second insulating substrate 40, a high-peak short-pulseoscillation-type carbon dioxide gas laser drilling machine manufacturedby Hitachi Via Engineering, Ltd. is used. A laser beam is directlyirradiated onto the copper foil 44 provided on the glass-cloth epoxyresin substrate 43 with a substrate thickness of 60 μm of the secondinsulating substrate 40 under the following irradiation conditions. Theopenings 46 for forming via holes each have a diameter of 75 μm and areformed at a rate of 100 openings/second.

(Irradiation Conditions)

Pulse energy: 75 mJ

Pulse width: 80 μs

Pulse interval: 0.7 ms

Frequency: 2,000 Hz

(7) Formation of Electrolytic Copper Plating Film

The surface of the first insulating substrate 30 is covered with aprotective film 48. Electrolytic copper plating is then performed on thesurface of the copper foil of the second insulating substrate 40 inwhich the openings 46 have been subjected to the desmear process, usingthe copper foil as a plating lead. The plating conditions are asfollows.

[Electrolytic Plating Solution]

Sulfuric acid: 2.24 mol/L

Copper sulfate: 0.26 mol/L

Additive A (reaction accelerator): 11.0 mL/L

Additive B (reaction inhibitor): 10.0 mL/L

[Conditions for Electrolytic Plating]

Current density: 1 A/dm²

Time: 65 minutes

Temperature: 22° C.±2° C.

In this plating process, the formation of an electrolytic copper platingfilm in the openings is accelerated by the additive A. On the otherhand, the additive B is mainly adhered to the copper foil part, and theformation of the plated film is suppressed. When the openings are filledwith the electrolytic copper plating film and the height thereofsubstantially becomes the same as that of the copper foil, the additiveB is adhered to the copper plating film and the formation of the platedfilm is suppressed as in the copper foil part. Accordingly, the openingsare completely filled with the electrolytic copper plating film, and theelectrolytic copper plating film exposed from the openings and thecopper foil substantially form a flat surface.

The thickness of a conductor layer composed of the copper foil and theelectrolytic copper plating film may be adjusted by etching. Thethickness of the conductor layer may be adjusted by a physical method,such as belt sanding or buffing, as required.

(8) Formation of Conductor Circuit and Filled Vias

After step (7), an etching resist layer (not shown) was formed on thecopper foil 44 of the second insulating substrate 40 and theelectrolytic copper plating film using a photosensitive dry film. Thethickness of the resist layer is in the range of 15 to 20 μm. The resistlayer is exposed using a mask having a pattern of a conductor circuitincluding lands of filled vias, and then developed. Accordingly, areasthat do not have the resist layer thereon are formed on the copper foil.

Subsequently, the electrolytic copper plating film and the copper foil44 on the above areas that do not have the resist layer are removed byetching with an etchant composed of aqueous hydrogen peroxide andsulfuric acid.

The resist layer is then removed by an alkaline solution. Furthermore,the protective film 48 applied on the surface of the first insulatingsubstrate 30 in step (7) is removed. Accordingly, a conductor circuit 50is formed on a surface of the second insulating substrate 40. Filledvias 52 that electrically connect the conductor circuit to the lands 41of the filled vias 39 provided on the first insulating substrate 30 arealso formed (see FIG. 4G). A dummy pattern, an alignment mark, a productidentification code, and the like may also be formed according to need.

(9) Formation of Recess for Accommodating Semiconductor Device

The resin area where the copper foil part has been removed by etching instep (4) is irradiated with a carbon dioxide gas laser to form anopening penetrating through the resin insulating layer 32 and reachingthe surface of the metal layer 42. The metal layer is exposed in theopening, and the side faces of the opening and the surface of the metallayer (serving as a bottom face) form a recess 54 for installing asemiconductor device 55 (see FIG. 5A).

In this example, in order to form the recess 54 for accommodating asemiconductor device in the first insulating substrate 30, a high-peakshort-pulse oscillation-type carbon dioxide gas laser drilling machinemanufactured by Hitachi Via Engineering, Ltd. is used. A laser beam isirradiated under the following irradiation conditions onto theglass-cloth epoxy resin substrate with a substrate thickness of 60 μm ofthe first insulating substrate, more specifically, onto the area wherethe copper foil on the surface of the first insulating substrate hasbeen removed. Accordingly, the recess 54 for accommodating asemiconductor device is formed. The recess 54 has a depth of about 100μm and dimensions slightly larger than the dimensions of thesemiconductor device to be accommodated.

(Irradiation Conditions)

Pulse energy: 100 mJ

Pulse width: 90 μs

Pulse interval: 0.7 ms

Frequency: 2,000 Hz

Regarding the recess 54 for accommodating a semiconductor device formedby laser machining, the metal layer 42 was exposed on the bottom face,the recess 54 had a substantially uniform depth, and the four corners ofthe recess 54 did not have an arch shape. The surface of the metal layeron which the semiconductor device is placed is a shiny surface.According to need, however, the surface of the metal layer may beroughened to some degree by a blackening treatment or the like. Thereby,the adhesiveness to an adhesive layer may be ensured.

Furthermore, the area of the recess is smaller than the area of themetal layer. Therefore, the depth of the recess can be easily madeuniform.

(10) Accommodation of Semiconductor Device Having Columnar Electrodes

A semiconductor device having columnar electrodes that is produced bythe following steps (a) to (d) is used as the semiconductor device 55accommodated and installed in the recess 54 of the substrate foraccommodating a semiconductor device, which is produced in steps (1) to(9) above.

(a) Preparation of Silicon Substrate

The following silicon substrate is prepared. Connection pads are formedon a silicon substrate (semiconductor substrate), which is in the formof a wafer. A protective layer (passivation film) is formed on areasexcept for the central part of each connection pad, and the central partof each connection pad is exposed on the opening provided on theprotective layer.

(b) Formation of Metal Underlayer

A metal underlayer composed of copper is then formed on the entire topsurface of the silicon substrate by sputtering so as to have a thicknessof 2 μm.

(c) Formation of Columnar Electrodes

A dry film resist composed of a photosensitive resin such as an acrylicresin is laminated on the metal underlayer to form a plating resistlayer having a thickness of 110 μm. The height of columnar electrodes tobe formed is set to about 100 μm.

The plating resist layer is then exposed using a mask having a patternof openings disposed at areas corresponding to pads of the platingresist layer, and developed. Accordingly, openings are formed on theresist.

Furthermore, electrolytic copper plating is performed using the metalunderlayer as a plating current path. Accordingly, columnar electrodescomposed of copper are formed on the copper underlayer disposed in theopenings of the plating resist layer.

Finally, the plating resist layer is removed, and the unnecessary partsof the metal underlayer are removed by etching using the columnarelectrodes as a mask.

Accordingly, the metal underlayer remains only under the columnarelectrodes.

(d) Formation of Sealing Film

A sealing film composed of an insulating resin such as an epoxy resin, apolyimide, or the like is formed on the top surface of the siliconsubstrate prepared in step (c). In this state, when the top surface ofthe columnar electrodes is covered with the sealing film, the surface isappropriately polished so as to expose the top surface of the columnarelectrodes.

Next, a dicing process is performed to produce semiconductor chips(semiconductor devices). In this case, the semiconductor device havingthe columnar electrodes has a thickness of 100 μl.

A thermosetting adhesive, for example, an adhesive composed of athermosetting resin produced by acrylating a part of an epoxy resin isapplied on the bottom face of the semiconductor device 55 produced insteps (a) to (d) to form an adhesive layer 56 having a thickness in therange of 30 to 50 μm.

Subsequently, the semiconductor device 55 was accommodated in the recess54 of the substrate for accommodating a semiconductor device, and a heattreatment was then performed at 100° C. to 200° C. to cure the adhesivelayer 56. Accordingly, a substrate 60 including the semiconductor device55 therein is produced (see FIG. 5B).

In this case, the leading end of columnar electrodes 58 of thesemiconductor device and the top face of the substrate are substantiallyon the same level. That is, the semiconductor device 55 is not tiltedand electrode pads are also flat.

(11) Lamination Process

An adhesive layer 62 such as a prepreg is disposed on the substrate 60produced in step (10). Furthermore, a single-sided copper clad laminatein which a copper foil 66 having a thickness of 15 μm is bonded on asurface of a resin insulating layer 64 having a thickness of 60 μm islaminated on the adhesive layer 62 (see FIG. 5C). Hot press is thenperformed in the direction shown by the arrows under the followingconditions. Accordingly, a multilayered substrate is formed (see FIG.5D).

(Conditions for Pressing)

Temperature: 190° C.

Pressure: 3.0 kgf/cm²

Pressing time: 35 minutes

(12) Formation of Openings for Forming Via Holes

Openings 70 and 72 for forming via holes are formed as in step (6). Theopenings 70 penetrate through a copper foil 66, pass a resin insulatinglayer 64, and reach the conductor circuit 41 that includes via lands andthat is provided on the first insulating substrate constituting thesubstrate for accommodating a semiconductor device. The openings 72penetrate through the copper foil 66, pass the resin insulating layer64, and reach the columnar electrodes 58 provided on the pads on thesemiconductor device (see FIG. 6A). The conditions for laser irradiationin this step are the same as those in step (6). Furthermore, a desmearprocess is then performed for the openings using a solution ofpermanganic acid.

(13) Formation of Electrolytic Copper Plating Film

Electrolytic copper plating is performed on the surface of the copperfoil wherein the openings have been subjected to the desmear process,using the copper foil as a plating lead under the following platingconditions.

[Electrolytic Plating Solution]

Sulfuric acid: 2.24 mol/L

Copper sulfate: 0.26 mol/L

Additive A (reaction accelerator): 10.0 mL/L

Additive B (reaction inhibitor): 10.0 mL/L

[Conditions for Electrolytic Plating]

Current density: 1 A/dm²

Time: 65 minutes

Temperature: 22° C.±2° C.

In this plating process, the formation of an electrolytic copper platingfilm in the openings is accelerated by the additive A. On the otherhand, the additive B is mainly adhered to the copper foil part, and theformation of the plated film is suppressed. When the openings are filledwith the electrolytic copper plating film and the height thereofsubstantially becomes the same as that of the copper foil, the additiveB is adhered to the copper plating film and the formation of the platedfilm is suppressed as in the copper foil part. Accordingly, the openingsare completely filled with the electrolytic copper plating film, and theelectrolytic copper plating film exposed from the openings and thecopper foil substantially form a flat surface.

The thickness of a conductor layer composed of the copper foil and theelectrolytic copper plating film may be adjusted by etching. Thethickness of the conductor layer may be adjusted by a physical method,such as belt sanding or buffing, as required.

Accordingly, the openings are completely filled with electrolytic copperplating film to form via holes connected to the conductor circuit andvia holes connected to the host of the semiconductor device.

(14) Formation of Conductor Circuit

After step (13), an etching resist layer is formed on the copper foiland the electrolytic copper plating film using a photosensitive dryfilm. The thickness of the resist layer is in the range of 15 to 20 μm.The resist layer is exposed using a mask having a pattern of a conductorcircuit including lands of filled vias and then developed. Accordingly,areas that do not have the resist layer thereon are formed on the copperfoil.

Subsequently, the electrolytic copper plating film and the copper foilon the above areas that do not have the resist layer are removed byetching with an etchant composed of aqueous hydrogen peroxide andsulfuric acid.

The resist layer is then removed by an alkaline solution. Accordingly, aconductor circuit 74 is formed on the resin insulating layer 64 coveringthe substrate for accommodating a semiconductor device, and filled vias76 that electrically connect the conductor circuit 74 to the lands 41 ofthe filled vias provided on the substrate 60 including the semiconductordevice 55 and filled vias 78 that are electrically connected to thecolumnar electrodes 58 provided on the pads of the semiconductor device55 are formed. A dummy pattern, an alignment mark, a productidentification code, and the like may also be formed according to need.

Furthermore, by repeating steps (11) to (14) as required, a multilayeredprinted circuit board including more layers can be produced.

In such a lamination, the substrates may be laminated so that thedirections of via holes are the same. Alternatively, the substrates maybe laminated so that the directions of via holes are opposite to eachother. The lamination may be performed in combinations other than thesecombinations.

(15) Formation of Solder Resist Layer

A solder resist layer 80 is formed on each outer surface of the topcircuit board and the bottom circuit board of the multilayered substrateproduced in steps (1) to (14). The solder resist layer 80 having athickness in the range of 20 to 30 μm is formed by applying a solderresist film or applying a solder resist with varnish whose viscosity isadjusted in advance.

The multilayered substrate is then dried at 70° C. for 20 minutes and100° C. for 30 minutes. A soda-lime glass substrate that has a thicknessof 5 mm and a chromium layer having a circular pattern (mask pattern) ofopenings of the solder resist is prepared. The solder resist layer 80 isthen exposed by irradiation of ultraviolet rays of 1,000 mJ/cm² whilethe soda-lime glass substrate is disposed so that the surface having thechromium layer is in contact with the solder resist layer 80.Subsequently, a DMTG development process is performed. The multilayeredsubstrate is then heated at 120° C. for one hour and at 150° C. forthree hours to form the solder resist layer 80 (thickness: 20 μm) havingopenings 82 (opening diameter: 200 μm) corresponding to the pad areas.

According to need, a roughened layer may be provided on each outersurface of the top circuit board and the bottom circuit board of themultilayered substrate prior to the formation of the solder resist layer80.

In this case, a dry film mask layer composed of a photosensitive resinis formed on the solder resist layer. The mask layer having a thicknessin the range of 10 to 20 μm is formed on the solder resist layer byapplying a mask layer film or applying a mask layer with varnish whoseviscosity is adjusted in advance.

The multilayered substrate is then dried at 80° C. for 30 minutes. Asoda-lime glass substrate that has a thickness of 5 mm and a chromiumlayer having a formation pattern (mask pattern) of the mask layer isprepared. Exposure is then performed by irradiation of ultraviolet raysof 800 mJ/cm² while the soda-lime glass substrate is disposed so thatthe surface having the chromium layer is in contact with the solderresist layer. Subsequently, a DMTG development process is performed. Themultilayered substrate is then heated at 120° C. for one hour to formthe solder resist layer (thickness: 20 μm).

(16) Formation of Corrosion-Resistant Layer

Next, the multilayered substrate having the solder resist layers 80 isimmersed in an electroless nickel plating solution (pH=5) containing 30g/L of nickel chloride, 10 g/L of sodium hypophosphite, and 10 g/L ofsodium citrate for 20 minutes. Accordingly, a nickel plating layerhaving a thickness of 5 μm is formed on the openings.

Furthermore, the multilayered substrate is then immersed in anelectroless gold plating solution containing 2 g/L of potassium goldcyanide, 75 g/L of ammonium chloride, 50 g/L of sodium citrate, and 10g/L of sodium hypophosphite at 93° C. for 23 seconds. Accordingly, agold plating layer having a thickness of 0.03 μm is formed on the nickelplating layer, thus forming a coating metal layer (not shown) includingthe nickel plating layer and the gold plating layer.

(17) Formation of Solder Layer

Subsequently, solder paste composed of Sn/Ag/Cu or Sn/Pb solder that hasa melting point of about 183° C. is printed on solder pads exposed onthe openings 82 of the solder resist layer 80 covering the top layer ofthe multilayered circuit board and ref lowed at 183° C. to form a solderlayer 84.

Example 2

A multilayered printed circuit board was produced as in Example 1 exceptthat a semiconductor device 55 that had an intermediate layer and thatwas produced by the following steps (a) to (c) was embedded in therecess 42 of the substrate for accommodating a semiconductor device.

(a) A chromium thin-film layer having a thickness of 0.1 μm and a copperthin-film layer having a thickness of 0.5 μm are continuously formed inthat order by sputtering in a vacuum chamber on the entire surface of asemiconductor device in which a protective layer is provided onconnection pads and a wiring pattern.

(b) A resist layer composed of a dry film is then formed on thethin-film layer. A mask having a pattern of the intermediate layer to beformed is disposed on the resist layer, and the resist layer is thenexposed. The resist layer is then developed to form areas that do nothave the resist layer thereon. A thick layer (electrolytic copperplating film) having a thickness of 10 μm is formed by electrolyticcopper plating on the areas that do not have the resist layer thereon.

(c) The plating resist layer is then removed by an alkaline solution orthe like. The metal film disposed under the plating resist layer isremoved with an etchant to form an intermediate layer on the pads of thesemiconductor device.

Accordingly, a semiconductor device having a length of 5 mm, a width of5 mm, and a thickness of 100 μm is produced.

Example 3

A multilayered printed circuit board is produced as in Example 1 exceptthat a taper is formed on the side faces of the recess for accommodatinga semiconductor device in step (9). In this case, in step (11) above, apart of the prepreg-containing resin insulating layer that covers thesemiconductor device accommodated in the recess fills the clearancebetween the side faces of the semiconductor device and the side walls ofthe recess. Accordingly, the resin insulating layer is integrated withan adhesive layer that fixes the semiconductor device on the bottom faceof the recess.

FIG. 7 is an example of a SEM image showing a cross section of therelevant part of such a multilayered printed circuit board. In thisexample, a dummy device is used as the semiconductor device accommodatedin the recess.

Example 4

A multilayered printed circuit board is produced as in Example 1 exceptthat the following substrate is used as the substrate for accommodatinga semiconductor device. The substrate is formed by laminating a firstinsulating resin in which a metal layer having dimensions correspondingto the dimensions of the semiconductor device is provided on one surfacethereof and a second insulating resin substrate in which an opening isprovided in an area corresponding to the metal layer in advance to forma recess in which one end of the opening is closed and the metal layeris exposed on the recess.

In the multilayered printed circuit boards according to the aboveexamples, satisfactory adhesiveness, electrical connectivity, connectionreliability, and heat-cycle resistance were ensured.

In the case where a taper angle was provided on the side faces of therecess, even when the accommodated semiconductor device was subjected toa thermal stress, an external stress, or the like in the lateraldirection, the stress could be relieved. Consequently, the heat-cycleresistance could be ensured. In addition, the phenomenon in which theadhesive used for fixing the semiconductor device was diffused along theside faces of the recess did not occur, and therefore, the adhesivenessof the semiconductor device to the bottom of the recess could beensured. In particular, it is believed that when the taper angle is inthe range of at least 60 degrees and less than 90 degrees, theadhesiveness is more reliably ensured.

In the embodiments of the present invention, a plurality of other resininsulating layers and conductor circuits may be formed on the resininsulating layer accommodating a semiconductor device. (For example, asshown in FIG. 8, additional two resin insulating layers may be formed onthe resin insulating layer including a semiconductor device.) In such astructure, via holes that electrically connect the semiconductor deviceto each conductor circuit can be formed.

In the embodiments of the present invention, as shown in FIG. 9, viaholes connecting to the metal layer may be formed in a resin insulatinglayer, and heat generated from the semiconductor device may bedissipated to the outside of the substrate through these via holes. Inthis structure, the via holes function as thermal vias.

INDUSTRIAL APPLICABILITY

As described above, the multilayered printed circuit board according tothe present invention provides a multilayered printed circuit board or asubstrate for mounting a semiconductor device in which a recess foraccommodating a semiconductor device is provided on a substrate andelectrical connectivity and connection reliability are ensured.

The invention claimed is:
 1. A method for manufacturing a multilayeredprinted circuit board wherein a semiconductor device is accommodated andfixed in a first resin insulating layer, a second resin insulating layerand a conductor circuit are provided on the first resin insulatinglayer, and the semiconductor device is electrically connected to theconductor circuit through via holes, comprising at least the steps of:forming a first insulating resin substrate by forming on a first surfaceof the first resin insulating layer at least a conductor circuit and ametal layer having a predetermined area corresponding to the dimensionsof the semiconductor device to be accommodated, forming on a secondsurface of the first resin insulating layer at least a conductor circuitand an area that does not have the conductor circuit thereon, the areahaving a predetermined area corresponding the dimensions of thesemiconductor device at a position facing the metal layer, and formingvia holes for electrically connecting the conductor circuit on the firstsurface to the conductor circuit on the second surface; bonding a secondinsulating resin substrate prepared by applying a copper foil on a firstsurface of a third resin insulating layer onto the first surface of thefirst insulating resin substrate under pressure to integrate thesubstrates; forming a conductor circuit on the first surface of thesecond insulating resin substrate and forming via holes for electricallyconnecting the conductor circuit formed on the first surface of thesecond insulating resin substrate to the conductor circuit formed on thefirst surface of the first insulating resin substrate; forming, on thearea of the first insulating resin substrate that does not have theconductor circuit thereon, a recess extending from the surface of thefirst resin insulating layer to the surface of the metal layer so as toexpose the surface of the metal layer; accommodating a semiconductordevice in the recess, and bonding and fixing the semiconductor device onthe surface of the metal layer exposed in the recess, with an adhesivetherebetween; and covering the semiconductor device, forming the secondresin insulating layer and a conductor circuit thereon, and then formingvia holes for electrically connecting the semiconductor device and theconductor circuit.
 2. The method for manufacturing a multilayeredprinted circuit board according to claim 1, wherein the recess is formedby laser irradiation so that the side faces of the recess form a taperedshape diverging from the bottom face upwards.
 3. The method formanufacturing a multilayered printed circuit board according to claim 1,wherein a columnar electrode or an intermediate layer is formed on a padof the semiconductor device in advance, and the pad is electricallyconnected to the via hole through the columnar electrode or theintermediate layer.